This invention relates to a wireless communication system in which one mobile node communicates via a plurality of wireless methods, and more particularly, to a fast switching technology between a plurality of wireless methods and to a cognitive wireless technology for improving a time space utilization efficiency of a radio spectrum.
Currently, a frequency band of equal to or less than 6 GHz (VHF, UHF, and low microwave band), which is suitable for mobile communication systems, is densely used for third generation cellular phones and wireless local area networks (LANs), bringing use of radio waves to an overload situation. Against the backdrop of such a situation, in order to secure a frequency band, which is required for mobile communications and is particularly high in needs, through utilizing the radio waves in the overload situation more effectively and efficiently, such a technology as to realize more sophisticated sharing of the radio waves among a plurality of radio wave utilization systems including mobile communications is sought after.
From a political perspective, “e-Japan Priority Policy Program-2004” (June, 2004) by the IT strategy headquarters of the Ministry of Internal Affairs and Communications describes that “We try to put to practical use by 2011 a wireless communication system that can establish an optimum communication environment by properly judging surrounding radio propagation quality and application requirements and by flexibly selecting a frequency band, a modulation method, a multiplexing method, and the like.” Accordingly, a technology for realizing such a system as described above is sought after.
In order to realize those technologies, as described in Mitola, “Cognitive radio for flexible mobile multimedia communications”, 1999 IEEE Int. Workshop on Mobile Multimedia Communications Digest (November, 1999) and Mitola, “Cognitive Radio: Making Software Radios More Personal”, 1999 IEEE Personal Communication, vol. 6, No. 4 (1999), the idea of “cognitive radio” that recognizes wireless conditions to control resources of a wireless system according to the conditions was presented in 1999. However, with regard to a method for realizing the cognitive radio, there are various types of approaches, and the examinations thereof have been currently conducted.
When communication is performed via a multi-mode wireless system, a base station transmits a beacon signal of a wireless LAN at given intervals, and a mobile node judges whether the mobile node is within a communication area of the wireless LAN (whether wireless LAN is available for use) by receiving the beacon signal. However, the wireless LAN is large in power consumption, and hence, as described in JP 2003-169379 A and JP 08-195754 A, there have been proposed technologies for more efficient power saving, in which a power supply is turned off when the wireless LAN is not used for a predetermined time period or a standby time is controlled. Those technologies employ a method in which the mobile node judges whether the wireless LAN is available for use by receiving the beacon signal. Moreover, JP 2004-320473 A describes a method in which a mobile terminal performs positional detection and, only when the mobile terminal is located in an area, a power supply concerning a transmitting/receiving section of a system is turned on. JP 2006-295643 A describes a method in which, when notification information for indicating absence of a radio LAN base station within a communication possible range is received from a mobile phone base station, no electric power is supplied to a radio LAN communication unit.